About one-fourth of the 300,000 annual deaths from sudden cardiac arrest take place outside of the home in public places. Traditional strategies for reducing these deaths have involved training lay persons to recognize cardiac arrest, to access the 911 system, and to perform cardiopulmonary resuscitation. Existing methods of emergency resuscitation have inherent time delays for a trained responder with defibrillation capability to get to the location of a person in cardiac arrest. Public access defibrillation (PAD), which involves placing automatic external defibrillators (AEDs) more widely in the community and training lay persons in their use, is one strategy for improving emergency treatment of victims of sudden cardiac arrest who collapse in public places. AEDs are known to work effectively to help victims of sudden cardiac arrest when the devices are used by trained emergency medical services personnel and other trained persons such as airline flight attendants. The primary objective of this research program is to examine the hypothesis that volunteers trained in the use of automatic external defibrillators for out-of-hospital cardiac arrest victims will significantly increase survival to hospital discharge, compared with community volunteers trained in standard life-saving techniques (recognition of cardiac arrest, 911 access and cardiopulmonary resuscitation). Other objectives include evaluation of neurological outcomes, quality of life, and cost effectiveness of public access defibrillation. This research is a multicenter controlled community study conducted in 1000 community units such as airports, residential apartments, shopping centers, senior centers, gated communities, office buildings, and sports venues. Volunteers in participating communities will be trained to recognize cardiac arrest, to access the 911 system, and to perform cardiopulmonary resuscitation. Half of the community units will also have AEDs placed in conspicuous locations, and the volunteers in those locations will be trained to use the devices. The research study is developed and conducted through collaboration among 20-25 field site subcontractors, a coordinating center, and the National Heart Lung and Blood Institute (NHLBI). This project serves as the coordinating center.